UNIVERSITY OF 
ILLINOIS LIBRARY 
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AGRICULTURE 


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Circulating copy < 


Agricultural Library 


| UNIVERSITY OF IDAHO 
AGRICULTURAL EXPERIMENT STATION 


Department of Entomology 


CIRCULAR NO. 25 MARCH, 1922 
| Published by the University of Idaho, Moscow, Idaho. 
SSS OOOO 


SPIDER MITES AFFECTING ORCHARD AND 
GARDEN FRUITS 


RALPH H. SMITH 


Spider mites are minute eight-legged spider- -like creatures which have 
sucking mouth-parts and feed on the juices of plants. Three species of 
importance occur in Idaho, namely, the two- spotted mite, the brown mite 
and the European red mite. 

With the aid of a small magnifier the three species may be identified 

‘by the following characters: 
- Two-spotted spider mite: Color usually pale green, pale lemon, or 
whitish with two dark spots and several bristles on the back, but not un- 
commonly the predominating color in late summer and autumn is orange 
or light red. It is the only one of the three species that spins webs. 


Brown spider mite: Decidedly larger than the above species. The 
predominating color is brown altho the legs and anterior end of the body 
are often pale reddish. The back is flat and without bristles. The front 
legs are neatly as long as the body and commonly are held close together 
in a straight line in front of the head. ’ 

European red mite: Slightly larger than the first species. The body 
is deep red. The back is strongly convex and set w ith a number of rather 
prominent long bristles. The larger bristles arise from small tubercles. 

The Two-spotted Spider Mite or “Red Spider.” ! 

This is the commonest and the most destructive of the spider mites in 
Idaho. It commonly has been called the “Red Spider” but the predomi- 
nating color usually is not red. The common name two-spotted mite is 
based upon the presence of two dark spots usually readily distinguishabie 
on the back of the full grown mite. Aside from attacking all kinds of 
orchard and garden fruits, it is an important pest of many garden, truck, 
and field crops. It also is a common pest of nearly all kinds of cultivated 
flowers, shrubs and shade trees. 


_ A Tetranychus. telarius Linn. 


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2 . IDAHO EXPERIMENT STATION 


Character of Injury 


The first indication of injury is the appearance of minute whitish flecks 


and fine webs on the leaves of affected plants. With continued infesta- 
tion the leaves usually turn grayish or yellow and the lower surfaces be- 
come covered with numerous fine webs under which the mites live. The 
webs collect particles of dust from the air and excrement from the mites, 
which gives the plants a dusty appearance. Eventually the foliage of in- 
fested plants becomes brittle and drops off. 


Life History 

Mature mites pass the winter on vegetation and in trash surrounding the 
plants which they infest during the summer. They become active on the 
first warm days in early spring. Migration onto the fruit trees begins 
soon after the blossom buds commence to open but it continues over a 
long period. Probably the greater number of mites go from surrounding 
vegetation to the fruit trees during May and the early part of June. 
Multiplication on the trees during the spring is very slow and studies show 
that serious infestations are not likely to develop before the first of July. 
During the latter part of August and in September the mites commonly 
collect in depressions on the fruit of prunes and plums. Later they mi- 
grate to the bases of the trees where they frequently make conspicuous 
web tents from which they gradually disperse to nearby vegetation. 


Control Measures 

The destruction of fallen leaves and other vegetation, and subsequent 
cultivation of the soil in berry patches are effective measures for destroy- 
ing the overwintering mites. Experiments in treating the surface soil 
about currant bushes with kerosene émulsion, miscible oils, and lime- 
sulphur gave no better results than was obtained by spading the surface 
soil. In clean cultivated orchards, surface cultivation in late fall and early 
spring as well as light cultivation during the summer months, apparently 


has retarded the development of infestations. Furthermore, orchards’ 


having neglected cover crops have been observed to be worse affected by 
the two-spotted mite than clean cultivated orchards or orchards having 
thrifty cover crops. 

When trees become seriously infested during the summer, the liberal 
use of irrigation water tends to reduce the injury. Direct control in 
orchards consists in spraying as soon as infestations become apparent, 
using commercial lime-sulphur 1 to 50. The lime-sulphur may be ad- 
vantageously combined with one of the codling moth cover sprays. Atomic 
sulphur, soluble sulphur, and wettable sulphur also have given good con- 
trol. The sulphur sprays have given good results on ‘small fruits. For 
small fruits which are soon to be picked the most satisfactory control has 


been to forcefully spray the plants with soapy water. In cities or wher- 


‘SPIDER MITES AFFECTING ORCHARD AND GARDEN FRUITS 3 


ever water pressure is available, thoro drenching of infested plants with 
the garden hose is an effective method of control. In spraying to control 
this mite it is essential that all surfaces of infested plants be entirely wet 
by the spray. Calcium caseinate spreader adds very materially to the 
effectiveness of the sulfur sprays. 


The Brown Spider Mite 2 
This mite, known also as the clover mite, has been observed in Idaho 
chiefly as a pest of orchard trees but in some parts of the United States 
it is particularly a pest of clover. It is generally distributed thruout the 
state and causes limited injury in most orchards each year. Occasional 
instances of serious injury have been reported. Unlike the two-spotted 
mite, the brown spider mite does not spin webs. 


Character of Injury 
— Injury usually becomes apparent soon after the blossoming period of 
apples and consists at first of white flecking of the leaves on short 
branches and fruit spurs borne directly on the primary brances of the 
trees. Under prolonged attack infested leaves become ashy-green and 
brittle. Instances have been observed where the younger foliage of pear 
trees turned brown and died completely. 


Life History 
In autumn the mites which have spent the summer on the foliage of the 
trees and others which migrate to the trees from nearby vegetation, de- 
posit minute red eggs on the bark. The eggs are placed in slight crev- 


Fig. 1—Winter eggs of the brown mite. Photograph taken April 10, 1921. 


2 Bryobia pratensis Garman; Recently resolved by Ewing into three distinct species. 


4 IDAHO EXPERIMENT STATION 


ices but frequently they are laid in such numbers as to cover large areas. 
of bark and give a decidedly red appearance to the trees. The eggs hatch. 
during a long period, beginning about the first of April and continuing 
until after the apple trees have bloomed. In 1921 a few newly hatched 
mites were observed on March 31 at Twin Falls but many eggs were yet 
hatching during the first half of May. A relatively small number 9f 
mites have been observed to hibernate about houses during the winter. 
These become active during warm days in February and March and at- 
tack grasses, flowers and such other green vegetation as they are able to 
find. Multiplication of the mites on fruit trees during the summer is 


comparatively slow. 


Control Measures 

Partial control has been obtained with the usual dormant ‘application of 
lime-sulphur. It has been found advisable in case of apples to delay the 
dormant application of lime-sulphur until just before the blossom clusters 
open, when many of the mites ordinarily will have hatched. 
Should the mites become injurious later in the season, spraying with 
sulphur as recommended for the two-spotted mite has given effective 
control. 


lig IIl—(A) European red mite. (B) Two spotted mite. (C) Brown | 
mite. All greatly enlarged. 


SPIDER MITES AFFECTING ORCHARD AND GARDEN FRUITS 5 


- European Red Mite 3 


The European red mite is strictly an orchard pest in Idaho, spending 
the entire year on fruit trees. It is generally distributed in southern Idaho 
and probably also occurs in the northern sections of the state. It has been 
observed to have several natural enemies which are potent factors in 
holding it in check. Two cases have come to the attention of Idaho Ex- 
periment Station officials in the past two years where orchards were re- 
markably heavily infested and the resultant injury was serious. The 
mites apparently favor apple trees on which to lay their winter eggs but 
during summer other orchard trees including pear, peach, apricot, necta- 
rine, plum, prune and cherry have been observed to be injuriously at- 
- tacked. It is believed that injury by this mite probably will be confined 
to local outbreaks occurring more or less periodically. 


Character of Injury 


The injury caused by the European red mite corresponds closely to that 
of the brown mite and consists chiefly in the minute flecking of the leaves. 
In instances of heavy infestation the leaves of plums and prunes have 
become ashy-gray and almost entirely devoid of green color. Unlike the 
injury caused by the two-spotted mite, there is not much tendency fer 
injured leaves to turn yellow. 


Life History 


Beginning about the first of September and continuing until the foliage 
of trees has been killed by freezing, bright red eggs are deposited on the 
bark in much the same manner as are those of the brown mite. The egg 
of the European mite has a smal! filament on the top which distinguishes 
it from-the egg of the brown mite. Sometimes the eggs are deposited in 
such large numbers as to form solid red patches on the bark of trees. 
Hatching begins about the time cluster buds appear on apple trees and is 
completed about a week after the petals have fallen from the blossoms. 
During the past two years the greatest number of eggs hatched just 
as the trees were in full bloom. The newly hatched mites occur chiefly 
on protected surfaces of leaves near the larger branches. In summer 
eggs are deposited on the leaves. 


3 Paratetranychus pilosus Can. and Franz. Determined by H. E. Ewing 


+ 


Fig. III.—The numerous white flecks which give this prune leaf a gray 
appearance are characteristic of the injury of the European red mute. 


Control Measures 


Several experiments were made for the purpose of determining a 
method of destroying the winter eggs with dormant sprays. On April 1, 
1921 a few days before eggs began hatching, different branches of trees 
bearing large numbers of eggs were sprayed as follows: 


No. 
No. 
No. 


1 


Scalecide 1:15. 

Scalecide 1:20. 

Scalecide 1:25. 

Dormant Soluble Oil, G, C. Co. 7 :100. 
Commercial liquid lime-sulphur, 5 degrees Baume. 


Commercial liquid lime-sulphur, 4 degrees Baume. 
Check, 


| 


SPIDER MITES AFFECTING ORCHARD AND GARDEN FRUITS 7 


No. 8 Commercial liquid lime-sulphur, 3 degrees Baume. 
No. 9 Distillate oil emulsion, G. C. Co. 6:100, 
No. 10 Kerosene emulsion 1:10. 

The four days following the application of the sprays, were bright 
with direct sunlight Summary of all observations showed that Nos. 4, 
9 and 10 gave decidedly better control than any of the other sprays, 
but even with these the control was not in any case above 70 per cent. 

On April 8 when the eggs were beginning to hatch in small numbers, 
different branches were sprayed as follows: 


No. 11 Concentrated washing lye 4 Ibs. to 100 gallons. 
No. 12. Concentrated washing lye 8 lbs. to 100 gallons. 
No. 13. Spray-emulsion 8 :100. 

No. 14. Dry lime-sulphur, S-W, 15:50. 

No. 15 Dry lime-sulphur, S-W, 30:50. 

No. 16. Dormoil 8 :100. 


Summary of observations up to May 5, showed that No. 12 gave 
slight control. No. 13 poor, No. 14 fairly good, No. 15 from 50 to 65 


per cent control, and No. 16 was about equal to No. 15. 


On April 17 when the eggs were hatching only in small numbers, dif- 
ferent branches of trees on which large numbers of eggs were deposited 
were sprayed as follows: 


Nor sib Check. 

No. 2b Soluble sulphur, Niagara, 1 lb. to 4 gallons. 

No. 3b Commercial liquid lime-sulphur, 5 degrees Baume. 
No. -4b° Miscible Oil No. 1, G. C. Co. 6:100. 

No. 5b Dormant soluble oil, G. C. Co. 7 :100. 

No. 6b -Scalecide 1:15. 

No. 7b Scalecide 1:20. 

No. 8b Scalecide 1:25. 

No; 9b. Check. 

No. 10b Distillate oil emulsion, G. C. Co. 6:100. 


No. 11b Kerosene emulsion 1:10. 

No. 12b Concentrated washing lye 8:100. 
No. 13b Spra-emulsion 8 :100. 

No. 14b Dry lime-sulphur S-W 15:50. 
No. 15b  Dormoil 8 :100. 

No. 16b_ Foraldehyde 1:50. 

No. 17b_ Foraldehyde 2:50, 


8 IDAHO EXPERIMENT STATION 


‘ 
i 


Observations EonHninine until May 5 showed that the oil Sprays: este 
better control than the sulphur sprays. 


One commercial orchard in which enormous numbers of eggs were de- 
‘posited was sprayed on April 1 and 2, with commercial liquid lime- 
sulphur testing 5 degrees and 6 degrees Baume. The spraying was done 
with unusual care but the treatment apparently had little effect on the 
hatching of the eggs. 


In experiments to destroy the mites after the trees had leafed ott, 
several spray substances were used, including commercial liquid lime- 
sulphur 1 to 50, soluble sulphur (Niagara) 1 to 20, flowers of sulphur 
1 to 10 with dissolved laundry soap at the rate of three pounds to one 
hundred gallons of spray added as a spreader, nicotine sulfate with 
laundry soap as a spreader and water alone. Commercial liquid lime- 
sulphur 1 to 50 with caseinate spreader also was added to the first codling 
moth cover spray. The results showed that spraying with water and with 
nicotine sulfate was of very little value in destroying the mites. Each 
of the sulphur sprays gave good control. The most satisfactory method 
of control was that of adding liquid lime-sulphur to the first codling 
moth cover spray at the rate of 1 to 50 and using caseinate as a spreader. 


Circulating copy 


Agricultureas Library 


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UNIVERSITY OF ILLINOIS-URBANA 
630.71D1C C005 
CIRCULAR 
25 1922 


NINN 


0112 019503 


